The Visual PathwayThe visual receptors send their impulses away from the brain, toward the center of the eye.First the bipolar cells gather the impulses from the rods and cones.Then the bipolar cells make synaptic contacts with ganglion cells.

The Visual PathwayThe axons of the ganglion cells join together to form the optic nerve, which makes a “U-turn” and exits the eye.There are no photoreceptors at the point at which the nerve leaves the eye. This is called the blind spot.You are not aware of your blind spot because information from the retina of each eye “fills in” the blind spot in the other eye. This integration occurs in the visual cortex.

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The Visual PathwayAt the optic chiasm, half of each optic nerve crosses to go to the opposite side of the brain.At this point the axons begin to separate, sending information to a number of locations in the brain.The greatest number of axons goes to the occipital lobe via the thalamus.

The Visual PathwayThe information from each retina is integrated in the visual cortex.Cortex receives input from both the left and the right retinas.Retinas focused on same point, input easily integrated.Conflicting images, cortical cells alternate msgs as they make sense of conflicting info.

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Color VisionDifferent wavelengths of electromagnetic energy correspond to different colors of light. There are three kinds of cones that respond to different wavelengths.Cells in the visual path process the information from these cones in terms of opposites.

Color VisionEach type of cone is most sensitive to a specific range of electromagnetic wavelengths.Short wavelengths are seen as blue.Medium wavelengths are seen as green.Long wavelengths are seen as red.

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Figure 4.12Figure 4.12Sensitivity of three types of cones to different wavelengths of light. (Based on data of Bowmaker & Dartnall, 1980)

Color VisionThe Opponent-Process TheoryTrichromatic theory does not account for some of the more complicated aspects of color perception.People experience four colors as primary – red, green, blue and yellow.People also report seeing colored after-images after staring at an object of one color. If you stare at a red object, you tend to see a green after-image when you stop staring.

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